Non-destructive system and method for detecting structural defects

ABSTRACT

A device for discovering, identification and monitoring, of mechanical flaws in metallic structures is disclosed, based on magneto-graphic/magnetic tomography technique to identify stress-related defects. The device can determine the position of the defect or stress including depth information. The device includes registration means that optimized for use with metallic structures of various types, shapes, and sizes. Applications include a real-time quality control, monitoring and emergency alarms, as well structural repairs and maintenance work recommendations and planning. Examples of the device implementation include pipes for oil and gas industry monitoring, detection of flaws in roiled products in metallurgical industry, welding quality of heavy duty equipment such as ships, reservoirs, bridges, etc. It is especially important for loaded constructions, such as pressured pipes, infrastructure maintenance, nuclear power plant monitoring, bridges, corrosion prevention and environment protection.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of the U.S. patentapplication Ser. No. 13/920,216 filed on Jun. 18, 2013, published as USPatent Application Publication No. 20140368191 A1 and granted as U.S.Pat. No. 9,176,096 B2 and U.S. Pat. No. 8,542,127. This application isalso a continuation-in-part of the U.S. patent application Ser. No.14/551,295 filed on Nov. 24, 2014, published as US Patent ApplicationNo. 20160146758 A1. This application is also a continuation-in-part ofthe U.S. patent application Ser. No. 14/867,538 filed on Sep. 28, 2015,published as US Patent Application No. 20160231278 A1. U.S. patentapplication Ser. Nos. 11/920,216; 14/551,295; and 14/867,538 are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates broadly to a non-destructive system andmethod for detecting structural defects as well as a device and methodfor continuous (extended) metallic structures inspection and monitoringfor possible defects; in particular, to contact and non-contact magneticscanner device and method, using magnetic tomography for a real-timestructural defects detecting; assessment of mechanical stress andcategorizing the defect by the level of danger.

Background Art

This invention can be used in various fields where constructions aretested for continuity defects and other stress concentrators as well asrisk-level safety factors in a contact fashion or combined with theremote method. Examples of device and method implementation may includepipes for oil and gas industry, detection of flaws in rolled products inmetallurgical industry, welding quality of heavy duty equipment such asships and reservoirs, detection of defects in bridges or cell towers,etc. It is especially important for inspection of loaded constructions,such as pressured pipes, infrastructure maintenance, nuclear power plantmonitoring, bridges, corrosion prevention and environment protection.

Railroads, electric transmission lines, bridges, cell towers, andpipelines have an important role in the nation's economy. Theseengineering structures do occasionally fail. Failure of these keyinfrastructure elements can cause economic disruption as well as putlives at risk.

Major causes of metallic infrastructure failure around the world areexternal interference, corrosion, and fatigue cracks; therefore,assessment methods are needed to determine the severity of such defectswhen they are detected in infrastructure, experiencing different loads.

Structures such as bridges, power transmission wires, wind turbines, andcell towers are important components of national infrastructure thatrequire maintenance and examination for defects in order to allowdetection of flaws that would result in failure. They are also allcharacterized in that these structures are often difficult to access dueto their height, length, and sometimes the additional local loads theycarry, i.e. bending, warping, exposure to wind, currents, etc. Bymounting non-destructive non-contact detection sensors to a drone onecan both conduct a thorough assessment of defects in the structure, ratethe defects in terms of likelihood to cause structural failure anddetermine the priority and necessity of repairs and do this assessmentwithout risk to human life as a drone equipped with sensors can accessthese places with greater ease than people can. For example, rather thanlowering a bridge inspector on a crane bucket to examine the undersideof a bridge a drone could be flown beneath the bridge and perform theinspection.

There are several magnetographic devices that have been disclosed fornon-destructive inspection of ferrous materials. In magneto-graphicinspection and defectoscopy the tested area of the material is placed inproximity to the magnetic medium. The changes of the surface-penetratingimpede flux due to the material flows or deviations can be recorded. Theresulting “magnetogram” of the material can provide the informationabout the location, size, and type of the defect or abnormality. Ingeneral, this information can be convened into the report about thequality of the material. Obtaining the magnetogram (magnetic picture) ofthe material in the course of the non-destructive inspection process isvery challenging and typically requires additional forms of inspection,such as roentgenogram or an X-ray image.

For example, U.S. Pat. No. 4,806,862 (Kozlov) offers a contact method ofmagnetographic inspection of quality of materials, where a magneticsubstance (such as liquid) is applied to be magnetized together with thetested material. According to the invention, the intensity of themagnetizing field is established by the maximum curvature of the surfaceof a drop of a magnetic fluid applied onto the surface of the materialto be inspected, so that the resulting magnetogram can be used to assessthe quality of the material.

In another magnetographic U.S. Pat. No. 4,930,026 (Kljuev), the flawsensor for magnetographic quality inspection is disclosed, whichincludes a flaw detector and a mechanism for driving themagneto-sensitive transducer. During the scanning procedure, themagnetic leakage fluxes penetrate through the surface of the material inplace where flaws occur, resulting in a magnetogram of the testedmaterial.

The deviations of F-value can be classified according to a level ofmechanical stress concentration—as follows: X1—for negligible detects(good technical condition of the metal); X2—for defects that requireplanned repairs (acceptable technical condition); X3—for defects thatrequire immediate repairs (unacceptable, pre-alarm technical condition,alarm).

The absolute values X1-X3 of the F-value (comprehensive value ofmagnetic field anomaly) should be defined for each particular case,depending upon the following factors: i) Material type (e.g. steel); ii)Topological location with the local background magnetic fields variationrange, iii) Distance to the object (e.g. pipe-line installation depth),iv) General condition of the deformation-related tension withinconstruction under testing, v) etc.

As a result, the only relative changes (variations) of the magneticfield can be evaluated, for the given defective segment (relatively tothe flawless segment), by comparing to its relative F-values. Thus, thevery moment of the ultimate stress-limit crossing can be identified foreach defective segment during the real operation (i.e. underpressure/loaded) condition. It can be done by monitoring the developmentof the defects within its F-value interval, namely, starting from thegood technical condition X1 up until the yield-strength limitapproaching and material breakdown. It provides a real possibility topredict the defect's speed development, resulting in increased accuracyin priority order definition for upcoming maintenance steps.

The aforementioned techniques are not satisfactory to be used forefficient prediction in defects development timeline and not capable ofproviding a real-time alert about the strength-limits approaching, i.e.when probable construction failure is about to occur.

The closest remote technology to the disclosed invention is shown in RU2264617 that describes the Magnetic Tomography (MT) technique. Thistechnique includes a remote magnetic field vectors measurement inCartesian coordinates with the movement of measuring device(magnetometer) along the pipe-line, the recording of the anomalies ofmagnetic field (on top of background magnetic field), processing of thedata and report on found pipe-line defects with their localization shownin resulting magnetogram. The technique provides a good sensitivity,also capable of discovering the following types of defects: i) Changingin geometry: dents, wavy surface, deformed shape of cross-section; ii)Metal loss, having mechanical, technological or corrosion nature;material discontinuity: layering and inclusions; iii) Cracks; iv)Welding, flaws, including girth weld defects. Moreover, such methodprovides a risk-factor ranking of the discovered pipe-line defectsaccordingly to material tension concentration (factor F). Accordinglythis technique was taken as initial prototype for the disclosedtechnology.

MT determines the comparative degree of danger of defects by a directquantitative assessment, of the stress deformed state of the metal.Conventional surveys only measure the geometrical parameters of adefect. Their subsequent calculations to assess the impact of the defecton the safe operation of the pipe do not take into consideration thestress caused by the defect. Therefore conventional surveys may fail todetect dangerously stressed areas of the structure or, conversely,classify a defect as one which requires urgent attention when, inreality, the stress level may be low and the defect presents noimmediate threat to the operation of the structure. Since MT directlymeasures the stress caused by defects it is an inherently more accurateguide to the safe operation of the structure than conventional surveymethods.

There are several methods for integrity assessment of extendedstructures (e.g. metallic pipes) that have been proposed in literature.Thus, U.S. Pat. No. 4,998,208 (Buhrow, et al) discloses the pipingcorrosion monitoring system that calculates the risk-level safety factorproducing an inspection schedule. There is another method disclosed inU.S. Pat. No. 6,813,949 (Masaniello, et al.), which addresses a pipelineinspection system having a serviceability acceptance criteria forpipeline anomalies, specifically wrinkles, with an improved method ofcorrelating ultrasonic test data to actual anomaly characteristics.

The main disadvantages of previous methods are: i) The scope of itsapplication is limited by large-scale linear objects and necessity tocontact the surface. Located at a considerable distance from each other,ii) Difficult real-time implementation of the device, iii) It isimpossible to identify the location of individual defects, visualize andspecify the exact position on the internal or external tested surfaces;iv) There is also a lack of visualization of the obtained information ina form of the resulting tomogram where all the locations of thedefective segments with associated respective risk factors (absolutemechanical stress values) are shown.

There is a need in developing a combination of contact and remotetechniques in order to increase sensitivity, resolution and visualrepresentation of the stress-related anomalies within the structure, aswell as a probability of operation failure (i.e. risk-factor).

The defect areas risk-factor criteria and ranking (such as materialstress: F-value) is used for planning a required sequence of repair andmaintenance steps. Such criteria were developed by comparing arisk-factor calculated using the defect geometry in calibration borepits with a predicted risk-factor obtained by the remote magneto-metricdata (i.e. comprehensive F-value of particular magnetic anomaly).

In the traditional method, there is no evaluation of cracks stability,that is, no prognosis for the rate of crack-like defects development,especially in a longitudinal direction. There is also no evaluation ofdanger of other types of defects (e.g. welds) due to operationconditions, as the evaluation of metal properties degradation inaggressive conditions and with anomalies of stress-deformed state (SDS)is not carried out. For example, there are bridge sections with sags,bends, stresses/stretches/twists, that is, with loss of a bridge orpipes stability. In addition, the main problem—the degree of stressconcentration in a particular bridge section—is not considered; it mustbe considered by engineers of the integrity department of thecompany/operator by e.g. expert evaluation, and it requires additionaldata about all local loads.

As an alternative to the above method, a magnetometric tomography method(MTM) has been proposed. MTM is a non-contact method of non-destructivetesting (NDT) and technical diagnostics based on remote scanning themagnetic field of a ferro-magnetic structure in a system of orthogonalcoordinates. Additionally, manual processing and calibrating are used todefine locations of sections with metal defects of various types andother stress concentrators, identify the type of the most dangerousdefects, and evaluate serviceability of defective sections according tothe degree of mechanical stress concentration.

However, MTM is currently available only to pipeline based application(both on-shore and under water). Also the current, detection capabilityof such a magnetometer is only up to a maximum distance of 20 times thestructural member diameter. Thus, such conventional MTM systems are notsuitable for many structures, which may be located at significantheight. The inspection speed is also limited to only about 2 meters persecond (m/s), and the recording of distance is typically manual. Also,the analysis of the collected data is substantially manual, i.e. itrelies again on expert evaluation.

A need therefore exists to provide a system and method for inspecting astructure with height or at altitude that seeks to address at least someof the above problems.

SUMMARY OF THE INVENTION

A device for discovering, identification of the danger level, risk-levelsafety factor and monitoring of mechanical concentrator (defects andloads) in extended metallic structure, such as pipe, a rail, a rolledmetal product, a reservoir, a bridge, a vessel, a cable, electricalpower transmission lines, or vertical pipelines, is disclosed. Thedevice includes a pulse generator being used to irradiate a part of themetallic structure, a sensor array registering a response from this partof the structure, video camera, odometer, gyroscope, a GPS, andaltimeter. The sensor array is located in proximity of the structure andmeasures its magnetic field gradient at a distance of up to 20 m fromthe structure without any surface preparation treatment. The sensorarray includes a number of 3-component arrays, positioned along the 3orthogonal dimensions. An analogue-to-digital converter digitizing thesensor signal which is wirelessly transmitted to the calculation unit.

A calculation unit exploits an inverse magnetostrictive (Villari) effectof changing material's magnetic susceptibility wider applied mechanicalstress. Such changing results in gradient distribution of the magneticfield along the area of the structure that has a magnetic field anomaly.The distribution, in turn, reflects a presence and a value of themagnetic field anomaly at the given location. An absolute value of themechanical stress, which corresponded to said anomaly, is furtherdeducted, thus characterizing a defect of the structure and stressconcentrators, optionally using, a pre-determined information such aslook-up tables, standards, thresholds or an alternative contactmeasurement such as a contact probe.

The sensor array functions without removing the non-metallic cladding ofthe structure, such as a concrete wall around a metallic pipe, or paintand other non-corrosive layers around structural bridge components, forexample. The sensor array measurements can also be performed from insidethe pipeline.

The device detects foreign objects that are present in vicinity of thestructure, measuring a relative distances and angles between themselvesand the found anomaly. The discovered information is visualized byrepresenting a topological map of the structure in real coordinates,showing simultaneously a structure layout, the foreign objects invicinity, the location and calculated three-dimensional values of themechanical stress.

The device is also capable of measuring a natural Earths backgroundmagnetic field without engaging the pulse generator. Such measurement issubtracted from the sensor signal to improve accuracy of the anomaly(s)location.

The device is operated by the battery with a residual charge indicatorto ensure a quality and reliability of the identification in the fieldconditions and can perform without interruption of the structure normaloperation.

A method for discovering, identification and monitoring of mechanicaldefects of various nature, causing the concentration of mechanicaltension in metallic structures, is also disclosed. The method includesirradiating a part of the metallic structure with electromagneticpulses, performing mechanical stress measurement of the metallicstructure by a sensor array placed in proximity of the structure andproducing a digitized sensor signal and digitizing the sensor signal.The method also includes analyzing the digitized signal in a calculationunit using the inverse magnetostrictive effect providing informationabout the presence and the value of the magnetic field anomaly caused byconcentration of mechanical stress at the given location of thestructure. The method calculates absolute values of the mechanicalstress around the anomaly, thus unveiling and characterizing the defectof the structure or additional local loads.

Accordingly, the present invention is directed to a system and a methodfor inspecting a structure which makes it possible to inspect thestructure at an altitude of 200 meters or more of a vertical structureor bridging structure with an accurate determination of the location ofthe defect area and its type. An object of the present invention is toprovide a system for inspecting a structure, comprising; a drone mountedmagnetometric tomography method (MTM) module movable adjacent thestructure for detecting a defect along the structure; and means fordetermining a position, including altitude, of the drone mounted MTMmodule, thereby determining the position, including altitude, of thedefect.

In one aspect of the present invention in the system the means fordetermining the position and depth of the drone mounted MTM modulecomprises means for determining the position and altitude of the dronemounted MTM module relative to a base station vehicle; and means fordetermining an absolute position of the base station vehicle and of thedrone. In another aspect of the present invention in the system themeans for determining the position including altitude of the dronemounted MTM module relative to the surface vessel comprises at least oneof an odometer, a Doppler velocity log, a pressure sensor, an altimeter,a gyroscope, a video camera, and a microelectromechanical systems (MEMS)accelerometer coupled to the drone mounted MTM module. In another aspectof the present invention in the system the means for determining theabsolute position of the drone and/or base station vehicle comprises aglobal positioning system (GPS) receiver. In another aspect of thepresent invention in the system time stamps of data from the dronemounted MTM module and the means for determining the position of the MTMmodule are synchronized based on a GPS time signal. In another aspect ofthe present invention the system further comprising means forcategorizing the defect based on at least a density of magnetic fieldstrength distribution along the axis of a structural member in ananomaly zone. In another aspect of the present invention in the systemthe means for categorizing the defect ranks the defect as one of one,two and three corresponding to immediate repair, scheduled repair and norepair, respectively. In another aspect of the present invention thesystem further comprising means for determining a safe operatingparameter of the structure. In another aspect of the present inventionin the system the drone mounted MTM module is disposed at least about 1meter from the drone engines.

Another object of the present invention is to provide a method forinspecting a structure, the method comprising the steps of detecting adefect along the structure using a drone mounted magnetometrictomography method (MTM) module adjacent the structure; and determining aposition of the drone mounted MTM module, thereby determining theposition of the defect.

In one aspect of the present invention in the claimed method the step ofdetermining the position of the drone mounted MTM module comprises:determining the absolute position of the drone mounted MTM module or theposition of the drone mounted MTM module relative to a base stationvehicle; and determining an absolute position of the base stationvehicle. In another aspect of the present invention the method furthercomprising synchronizing time stamps of data from the drone mounted MTMmodule and equipment for determining the position of the drone mountedMTM module based on a GPS time signal. In another aspect of the presentinvention the method further comprising categorizing the defect based onat least a density of magnetic field strength distribution along apipeline axis in an anomaly zone. In another aspect of the presentinvention the method further comprising ranking the defect as one ofone, two and three corresponding to immediate repair, scheduled repairand no repair, respectively. In another aspect of the present inventionthe method further comprising determining a safe operating pressure ofthe pipeline. In another aspect of the present invention the methodfurther comprising determining a safe operation term of the pipeline.

The present invention makes it possible to determine the exact locationof the drone mounted MTM module on the structure when you move it in theair along the structure and thus pinpoint the location of the defect, ifit is registered.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be discussed in further detail below withreference to the accompanying figures in which:

FIG. 1 shows a block-diagram of the device for discovering,identification and monitoring of mechanical defects in metallicstructures using contact method, optionally, in combination with anon-contact technique.

FIG. 2 shows a general principle of operation of the contact andnon-contact magneto-graphic techniques used in metallic structuredefects monitoring and integrity assessment.

FIG. 3 shows an example of a single magneto-graphic measurement. Thediagram represents the three areas of a magnetic field anomalies (a),(b) and (c) corresponding to the respective local mechanical stresses.The area (c) shows the evidence of the metal stress yielding-limitcrossing.

FIG. 4 shows a block-diagram for metallic structure integrity assessmentand maintenance planning method.

FIG. 5 shows at block diagram illustrating a computing device forimplementing the method and system of the example embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention describes the contact magnetic scanner device thatuses a magnetic tomography (MT) for contact magnetographicidentification and analysis of mechanical flaws/defects, optimized forextended metallic constructions inspection. The invention can be used incombination with a non-contact identification. And can be applied tovariety of extended metallic structures, such as a pipe, a rail, arolled metal product, as reservoir, a bridge, as vessel, a cell tower, acable, or electrical power transmission lines.

The use of MT device has following advantages: 1) Applicable forinspecting structures that are otherwise difficult or dangerous toinspect; 2) the objects to be inspected include but not limited to:compressor stations, oil refineries, chemical plant pipelines, airportpipelines under concrete and asphalt pavement, pipeline inclusions,water-supply pipelines in cities, variety of extended metallicstructures, such as a pipe, a rail, a rolled metal product, a reservoir,a bridge, a vessel, a cell tower, a cable, or electrical powertransmission lines; 3) the use of MT device does not require anypreparation of the structure for testing such as digging, cleaning,removing coatings, stopping fluid flow, or stopping structure operation;4) the use of MT device does not require magnetizing of the object'sstructural members; 5) MT device capable of detecting flaws of varioustypes including long crack-like structural member defects, fatiguecracks, stress cracking (SCC) and welding defects; 6) the use of MTdevice does not have limitation on the structure diameter or thickness,configuration and protective coatings, for example, change of pipediameter/wall-thickness, turns and their directions, transported product(e.g. gas, oil, or water, electricity), inside pressure, pipelineprotection e.g. cathodic protection, etc), type of cover (soil, water,asphalt, concrete, ice), etc, as well as structures in the housings(cartridges) of type “pipe in pipe” (if you can change the operatingpressure in the inner tube—it is possible to distinguish betweenanomalies of the internal working of the pipe from the outside—housing).

The MT device is capable to evaluate the degree of danger of defects andrisk safety factor by the level of concentration of mechanical tensionsrather than defect geometry (e.g. length-width-depth) and particularlysuitable for running a database on condition certification of objects ofany length and any monitoring period.

The MT device implementation guarantees minimal customer resources usefor monitoring preparation and repair works such as: i) reduces workvolume and total costs of structure access works; ii) greatly reducestime of full diagnostic—repair evaluation—repair planning (fitness forservice)—repair cycle; iii) gives structure corrosion and integrityprognosis and estimates levels of tense-deformed state of the structureunder current operating conditions.

The MT device application provides a remote metal flaws monitoring,which is particularly suitable for hidden ferromagnetic constructions ofextended length.

The general combined block-diagram of the method is given in FIG. 1.

The magnetic tomography device is based on using of the inversemagnetostrictive (Villari) effect—i.e. the changing of the materialmagnetic susceptibility under applied mechanical stress. Generally, suchtechnique uses “natural” magnetization of the ferrous installations bymagnetic field of the Earth. The changing of magnetic susceptibilityresults in distribution of magnetic field gradient along the structuresurface area under measurement, thus providing information about thepresence and the value of the magnetic field anomaly at the givenlocation of the structure.

The term “contact measurement”, as used herein is defined as themeasurement being used from a small distance from the surface of thestructure under testing. For the preferred embodiment of the invention,such distance is defined as a small if it is less than 20 cm from thesurface of the structure. Furthermore, for the preferred embodiment ofthe invention applying an additional (pulsed) magnetic field is used.

The term “remote measurement”, as used herein is defined as themeasurement being used from a substantial distance from the structureunder testing. Unlike to the contact measurement (non-destructive ordistractive), the remote sensor is not necessary located in a closeproximity to the structure. For the preferred embodiment of theinvention, the substantial distance have value of 1-25 m, making thedisclosed device especially effective for testing structures locateddeep underground, underwater, or at a significant height.

The remote measurement is capable of identifying the anomalies bydeviation of the Earth's magnetic field at each location from abackground value, without applying an additional magnetic field duringthe measuring.

The contact measurement device is also capable localizing coordinates offoreign objects in vicinity of the structure and making a linkagebetween the anomalies' locations and the foreign objects locationsaround the structure. In the preferred embodiment of the invention, thedevice finds coordinates of foreign objects which can be present invicinity of the structure and measures a distance/angle between thoseforeign objects and the structure's anomaly.

Both remote and contact measurements are further capable of localizingcoordinates of the structure and detecting anomalies with localizedcoordinates within the extended metallic structure based on measuring avalue of the Earth's magnetic field at multiple locations in vicinity ofthe structure.

The present invention discloses the Contact Magnetic Scanner a devicefor the contact detection of the defects in metallic structures. Thepresent invention effectively overcomes the aforementioned disadvantagesof contact detect monitoring and detection.

Similarly to the remote method, the contact method at a givenmeasurement point, the presence of the magnetic field anomaly and itsmagnitude (the local stress at the remote area) is determined based on acomparison between the increments (modules) of the Earth's magneticfield values (magnetic moments). Such calculation method is based on adipole approximation of the remote stress-concentrator. The solution ofthe problem of the magnetic moment calculation results from a system ofalgebraic equations, which, for example, described in the patent U.S.Pat. No. 4,309,659.

The disclosed device expands the scope of device applications fordifferent types of metallic structures (e.g. confined extended, smalland large), ii) provided real-time operational means by including, datapreprocessing and calibration, iii) increases the identificationsensitivity of the defects located at the surface and within the volumeof the object by including an additional pulse-magnetization unit, v)using a contact tomography technique in order to add 3D visualizationcapabilities using a 3D model of the tested object. The informationvisualization (display) unit of the device represents a topological mapof the structure in real coordinates, showing; simultaneously astructure layout, the foreign objects in vicinity, the calculated valuesof a mechanical stress and the location of the found anomalies.

The disclosed device uses pre-determined information for structureanomaly identification and localizing. Such pre-determined informationcan be a look-up table, preset standards and thresholds, an alternativecontact measurement, or combination of the above.

Moreover, the device can combine a contact and non-contact measurementincreasing the reliability and accuracy of information about thenecessary repair or stop alarm. It can be done using the risk-factorranking tables based on the absolute values of stress, compared againstthe values from regulatory documentation (for particular object).

In the preferred embodiment of the invention, the device performs theidentification of anomalies without interruption of the structure normaloperation.

Increasing the efficiency of the method by applying a 3Dvisualization-assisted maintenance and repair schedule with the realvalues of mechanical stress) to the actual structural layout, such as abridge integrated into the existing topology.

Such technological outcome can be achieved, mainly, due to the followinginnovative means: i) Contact (object surface) identification of thelocal defects and their respective risk-factors; ii) Comparing theremote measurement with ones obtained locally; iii) Comparing theresulting measurements against the values from regulatory documentation(for the particular object), iii) Graphical 3D visualization of theobtained information using the actual topological layout of the area andthe structure in absolute geographical coordinates.

For the remote registration of magnetic field anomalies in extendedmetallic structures (such as a bridge) is performed in a predeterminedcoordinate system relatively to the structure with a known (fixed)remote sensor array aperture. The coordinates of each single measurementalong the structure can be chosen accordingly to the cross-section sizeand burial depth or height of the structure. It results in the matrixdistribution of magnetic field gradient along the structure surface areaunder each single measurement. The presence and the value of themagnetic field anomaly at the given location are derived from thecomparison of different increments of the Earth's magnetic inductionvector modulus.

Similarly to the remote measurements, the contact measurement alsoincludes device to measure the magnetic field vector in Cartesiancoordinates, by moving the registration device (magnetometer) along(above, below, or to the side of) the metallic structure (of arbitraryconfiguration, in general) and registration of the magnetic fieldanomalies. Such anomalies are calculated by a deviation from thebackground values (calculated using matrix transformations).

The contact device also connected the data recording unit and decodingsystem that provides conclusive information about the presence andlocation of the defects in the form of magnetograms that shows thelocation of the defective pipe sections and their degrees of risk.

Similarly to the remote measurements, the contact measurement of theextended object (such as bridge) uses the recording of the magneticfield that is carried out in a pre-defined coordinate system atspecifically defined measuring points by a set of sensors having apre-selected aperture (base) K2. This aperture corresponds to the axisof the extended object with a measuring step K1.

The exact location of measurement points is defined from the width andheight (e.g. of the bridge), using coefficients K1, K2 and K3, where:K1—is the measuring step (registration of the magnetic field induction)0.2 in, for example, K2—the aperture (the base) of the sensors, chosenfrom the ratio 0.7 D≦K 2≦l, 4 D, where D—is the diameter or width of thestructure (pipeline), K3—is the depth or height of the structure, or theshortest distance from the metallic construction to the surface. [m]

In the case of a non-linear (or small) extended object the contactregistration c the magnetic field is carried out in a fixed coordinatesystem. In this case, registration is possible at different relativepositions of the sensors and their arbitrary orientation with respect tothe object (coplanar or collinear).

To verify the anomaly angular position along the structure (pipeline)circumference, the angular scanning step K1 should not larger than 30degrees with the pre-defined distance between the sensors K2, to ensurethe required accuracy of calculations.

The block-diagram of such device is shown in FIG. 1, with the referenceto FIG. 1, the device for contact and, optionally, non-contactmeasurements comprises of a sensor array for remote measurements (1), asensor array for proximity (contact) measurements (20), a quartzgenerator (2), a frequency divider (3), analogue-to-digital converter(A/D) (4), a control unit (5), a threshold unit (6), a light- andsound-alarm unit (7), a battery with a charge indicator (8), acalculation unit (9), a (resulting) information unit (10) with a displayunit (23), a non-volatile memory unit (11), a recording unit (12), acase-analysis unit (13), a pulse generation lint (21), an odometer unit(23), a GPS unit and pressure sensor(s) (14), navigation unit(accelerometer/odometer) (17), gyroscope (20), altimeter (21) and alogic unit (15). The device performs in a following manner.

The remote sensor array (1) registers induction gradients of themagnetic field (16) within construction under testing.

The proximity sensor array registers induction gradients of the magneticfield, the gradients corresponding to reflections of the EM pulses fromthe structure; the EM pulses generated by the Pulse generator. Thesignal from the proximity sensor is used as a calibrating measurement.

By using A/D converter (4), the both digitized signals (remote andcontact) are: i) inputted into calculation unit as a preliminary data;ii) recorded by the memory unit (11). The Quartz generator (2) controlsthe frequency of the A/D converter (4).

The control unit (5) through the logic unit (15) controls the caseanalysis unit (13) with predetermined database and lookup tables, therecording unit (12), the GPS unit (14), the navigation unit (17),gyroscope (20), altimeter (21) and the memory unit (11).

The calculation unit (9) receives the information from units (12), (13),(14), (17), (10), (21) through the memory unit (11), controlled by logicunit (15).

The real-time information from (4) is compared with the information fromthe threshold unit (6). By these means, the visualization of thereal-time data against the threshold values is provided, enabling thealarming (by the unit (7)) an operator about potentially dangerousoperational conditions of the structure. The remaining charge of thebattery (8) is monitored. The calculation unit (9) is responsible forthe information processing, providing the information to the resulting,and visualization unit (10).

The calculation unit (9) unit receives the digitized signal, uses theinverse magnetostrictive effect of changing of material magneticsusceptibility under applied mechanical stress resulting in gradientdistribution of the magnetic field along an area of the structure thathas a magnetic field anomaly, the distribution of magnetic fieldgradient providing an information about a presence and a value of themagnetic field anomaly at the given location of the structure and amechanical stress, corresponded to the anomaly.

The calculation unit (9) further calculates absolute values of amechanical stress around all found anomalies in the metallic structureusing, the measured values of the Earths magnetic field for each anomalyand applying the calibration coefficient. As a result, the calculationunit is capable of identifying and localizing of said signal anomalies.

In one embodiment of the invention the calculation unit is located at adistance from the sensor array, and the digitized signal is transmittedto the calculation unit via wireless connection.

The measured magnetic field values from 2 inputs (16) and (19) localstress at the remote area are recorded at each measurement point, (bothfor contact and optional remote sensor independently), then furthercompared with other measurements within a respective segment of themetallic construction. By these means the anomalies (levels ofstress-deformation) that deviate from the baseline magnetic field valuesare selected. Thus, the location of each stress-related deformation isderived from the maximum concentration value of the magnetic field aftercomparing it with the previous measurements.

The visualization unit has a 3-dimensional display means in order toprovide a 3-D representation of the density of magnetic field strengthdistribution, found detects and its risk-factors along with thetopological (3D) map of the structure under testing.

The resulting and visualization unit (10) also accommodates inputs fromthe threshold unit (6) and the light-/sound-alarm unit (7) which enablesidentification of the parameters' deviation from the background level,as well as (e.g. wirelessly) informing an operator about the deviationvalue in real-time, respectively.

Moreover, the resulting and visualization unit (10) is capable ofcomparing the remote signals (19) with in-contact measurement (18) andproducing a set of calibration coefficients in order to calibrate theresulting calculated data of found magnetic anomalies.

The situational case-analysis unit (13) enables the analysis of theinformation in the context of pre-determined technological informationand schemes, which, in combination with the GPS unit, navigation unit,gyroscope, and altimeter sensor(s) (14, 17, 20, 21), provides moreaccurate topological mapping.

In the preferable configuration of the device, a GPS sensor (14) iscomplemented by a navigation unit (17) and gyroscope(s) (20) and/or setof accelerometer(s) (17), and odometer unit (17) enabling the recordingof the device's angle-positioning relatively to the extended metallicstructure cross-section at each moment of the magneto-graphicalmeasurements. The recorded angle-positioning data (includingpositioning, relatively to horizon) is used further to correct themagneto-graphical measurements due to structural bending/turning-relateddeviations.

Accordingly, the absolute coordinates of discovered defects relativelyto the (visible) reference objects can be obtained with the followingregistration in the database during the equipment assessment report.

In the preferable configuration of the mentioned device, each sensorarrays (1) and (19) consist of a few 3-compenent arrays, positionedalong the 3 orthogonal dimensions. Alternatively, each array includes afew single-component sensors, such as optically pumped quantumanalyzers. Using the optically pumped quantum analyzers in the sensorarray (1) allows higher flaw-detection accuracy in undergroundconstructions, well-suited for detecting relatively small values ofmechanical stress, and/or deeper underground installation.

Since sensor arrays (1) and (19) can be rotated above the surface of thestructure during the scanning procedure, it is possible to implement apolar coordinate system for detects detection, in combination with thedata from the gyroscope (20) and navigation/accelerometer/odometer unit(17).

The recording process is arranged in a discrete manner, enabling anindependent storage and access for different recorded portions (memorysegments) of the scanning.

In the preferable configuration of the disclosed device, the calculationunit (9) calculates: i) magnetic field gradients distributed along thesquare area within the defined segment of the structure, ii) the valuesof the local mechanical stress within the defined segment of thestructure.

The device allows identifying the location of defects using bothin-contact and remote magnetic measurements.

Moreover, it expresses the calculations in real-time, also providing thevisualization of the information in the form of tomograms with referenceto the 3D model of the controlled object.

Moreover, the device provides automated evaluation of the defects riskfactor at respective identified location, allows automatic processing,interpretation and archiving of non-destructive testing results.

In the alternative configuration of the disclosure, the calculation unit(9) can be realized similarly to the U.S. Pat. No. 4,309,659 patent.

Moreover, in the alternative configuration of the disclosure, therecording unit (12) can be realized similarly to the RU2037888 patent.

The principle of operation of the device shown in FIG. 1, is explainedfurther in FIG. 2. The FIG. 2 a shows the structure (201) withoutdefects, with the preliminary magnetic tomography charts (magnetogram)(202) showing the measured background (calibrated to zero) level ofmagnetization. The FIG. 2b shows the same structure (201) with thepotential defects (203), (204) corresponded to the deviations of thetomography charts (205). The FIG. 2c show the same structure (201) withthe processed tomography charts (205) showing the location of the defect(204) that require an immediate attention (unacceptable, pre-alarmtechnical condition, alarm), based on the local mechanical stress valueestimate.

As mentioned before, the magnetogram (202) attributes and characterizesthe section of the structure by registering and analyzing changes in themagnetic field of the structure such as a bridge. These changes arerelated to stress, which, in turn, is related to defects in the metaland insulation. Magnetic measurements data is collected from the surfaceand includes the detected anomalies. Such detected anomalies arefunction of a local stress and/or local mechanical tension andstructural changes in the metal. Moreover, a post-processing of thisexperimental data enables the visualization of the flaws in thestructure.

The device can operate on the metallic structure which is covered by anon-metallic cladding and the sensor array performs the measurementwithout removing the cladding. Moreover, the device (sensor array) iscapable of performing measurements from within the structure, such asbetween bridge beams and girders.

The described MT device does not measure the dimensions of geometricdefects alone, but, instead, provides a stress measurement caused bythese defects and identifies their character, location and orientationin accordance with the location and orientation of the area of stress.Linear and angular coordinates of flaws in the metal and coating havebeen experimentally defined within a tolerance of +/−0.25 m.

The device explained by FIG. 1 and FIG. 2 can effectively identify andanalyze the magnetic field anomalies in areas with stress concentratorscaused by: i) defects or changes in structural conditions (such as metalloss, cracks, dents, lamination and inclusions); ii) erosion, seismicactivity, or third-party damage.

FIG. 3 shows the example of a single magneto-graphic measurement. Thediagram represents the three areas of a magnetic field anomalies (a),(b) and (c) corresponding to the respective local mechanical Stresses.The area (c) shows the evidence of the metal stress yielding-limitcrossing.

In parallel, the in-contact (proximity) defectoscopy has been performedat the location (c). The actual dimensions of defects (cracks andcorrosion) have been evaluated. The magnetographic device calibrationhas been done based on a difference between the measured signal (versusbackground) and the actual parameters of the defect(s) found. Then, thecalibrated values of the anomalies have been used as a criterion. Forthis particular case, the calibrated values appeared to be 3-10 timeshigher comparing to the background signal value. The follow-upmagnetographic measurements has been performed in a real-time.

the presented MT device helps to plan necessary structural maintenanceprocedures and define their priorities. The device is particularlyefficient when the magneto-graphic material (Magnetic Tomography)inspection is applied to extended metallic constructions, revealing itsflaws against the topological map of the structure.

Moreover, the device enables direct monitoring of the defectiveconstruction segments with still acceptable technical conditions. Itallows a long-term database support for the follow up monitoring,certification, prognosis and operational timeline for the structure.

The present invention also describes the magnetographic methodmaintenance timeline planning method (priority steps), optimized forextended metallic constructions. The block-diagram of the method isgiven in FIG. 4.

The method includes (with reference to FIG. 4): Precise scanning (401)using the non-destructive magneto-graphic (such as MT) anomaliesdetection technique (412) for (axial) localization of the extendedmetallic structure (e.g. subterranean or submarine pipeline), as well assurrounding scanning (402) for identification of other possible objectsin the vicinity of the structure, including hidden objects (pipes,cables) detection (424) and identification of the defective segments orareas of the said structure, in general, by using thermo-visual imaging,magneto-graphic methods or by other remote (non-contact,non-destructive) methods; accurate location of different types ofanomalies by using thermal and magnetic non-contact scanning sensorsmoving in Cartesian coordinates. Registering and processing of theobtained data and assessing resulting anomalies in accordance with theirrisk-factor and structural topology (mapping) (403). Identification ofthe absolute geographical coordinated for characteristic elements of theconstruction under testing (403), preferably by using a GPS sensor(s)(413) and altimeter (416) and (inertial) navigation system (gyroscopeand/or accelerometers) (415). Non-contact detection (424) of theconstruction defects and flawless segments. In-contact measurement of atleast one found defect (405) (e.g. visual, spectral, magneto-graphic).Calculation of the local metal stress at each found anomaly (406) andcalibration (407), using calibrating coefficients obtained by in-contactmethod (405) and regulatory documentation and stress/risk look-up tables(409). Processing the obtained information about discovered defects andits ranking accordingly to the risk factor (value of mechanical stress)(408). Graphical visualization of the results in the form of thetopological map of the construction using absolute values ofgeographical coordinates (410). The topological map would reflect themaintenance schedule to be applied to the construction following fromthe recorded mechanical stress values at the defective segments of theconstruction (409), (410). The method includes preventive warning means(414) to inform about defects that require immediate attention. e.g.unacceptable operational condition. The aforementioned method providesoperational and monitoring prognosis (411) with an optimal priorityplanning for required maintenance steps for construction under testing.

In the preferred embodiment of the invention the non-destructivedetection of anomalies in the structure is performed usingmagnetographic technique such as MT.

The main goals of the present invention are: i) to increase the method'sapplicability area: ii) to increase the accuracy of the priorityscheduling for required maintenance and repair procedures iii) tobroaden the spectrum of the potentially scheduled repair procedures,based on the additional data.

The invention is a system for inspecting a structure which has a dronemounted magnetometric tomography method (MTM) module for detecting adefect or stress along the structure; an altimeter sensor fordetermining a height of the drone mounted MTM module.

The system further having a module with a sensor array with at leastthree sensor positioned in three orthogonal dimensions.

The system further having a compass for registering azimuth data of thedefect and stress position on the structure at the determined height.

The system wherein the system outputs a 3D map of the inspectedstructure on a computer screen; the map showing the defects and stressconcentrator.

The system further having means for categorizing the defect andcondition stress effect based on at least a density of magnetic fieldstrength distribution along a structure axis in an anomaly zone.

The system further having a camera for registering an image of thedefect, which is visible or non-destructive testing (NDT) ornon-destructive examination (NDE) tools for hidden defects (HanpHMep,internal corrosion) and causes of additional loads (e.g., free slack orloading landslides in the mountains).

The system further having additional means for determining a position,including height via altimeter sensor, of the drone mounted MTM modulerelative to a sea surface and relative to a linear coordinate ofstructure axis comprising, at least one of an odometer, a Dopplervelocity log and a microelectromechanical systems (MEMS) accelerometercoupled to the drone mounted MTM module.

The system further having an engine for moving the sensors along thestructure adjacent to the structure.

The system wherein a distance between the sensors and a surface of thestructural member is from 0, being on the surface of the structuralmember, to a distance equal to 15 times a diameter (up to 25 m) or widthof the structural member.

The system further having a range finder to determine a distance betweenthe sensors and the surface of the structural member.

The system further having a control unit to adjust operation of theengine in order to keep the distance between the sensors and the surfaceof the structural member from 0, being on the surface of the structuralmember, to a distance equal to 15 times a diameter or width of thestructural member.

The system further having a processing unit.

The system wherein the means for categorizing the ranging of dangerousas one of one, two and three corresponding to immediate repair,scheduled repair and no repair, respectively taking account stressconcentration, stress effect, material strength, condition stresseffect, or stressing sequence.

The system further having means for determining a safe operatingparameter of the structure, taking into account stress concentration,stress effect, material strength, condition stress effect, or stressingsequence.

The system further having means for determining a safe operation term ofthe structure.

The system wherein the drone mounted MTM module is mounted to a remotelyoperated drone.

The system wherein the drone mounted MTM module is disposed at leastabout 1 meter from drone engines.

The invention also providing a method for inspecting a metallicstructure, the method comprising the steps of detecting a defect orstressing along the structure using a drone mounted magnetometrictomography method (MTM) module adjacent the structure; determining aheight of the drone mounted MTM module by use of an altimeter sensor;and determining, a position, including height via altimeter sensor, ofthe drone mounted MTM module, thereby determining the position,including height via altimeter sensor, of the defect or stressconcentrators.

The method wherein the step of determining the position, includingheight via altimeter sensor, of the drone mounted MTM module comprises:determining the position, including height via altimeter sensor, of thedrone mounted MTM module relative to a base station vehicle or absoluteposition of the drone mounted MTM.

The method further involving synchronizing time stamps of data from thedrone mounted MTM module and equipment for determining the position,including height via altimeter sensor, of the drone mounted MTM modulebased on a GPS time signal.

The method further involving categorizing the defect based on at least adensity of magnetic field strength distribution along a structure axisin an anomaly zone.

The method further involving ranking the defect as one of one, two andthree corresponding to immediate repair, scheduled repair and no repair,respectively.

The system further involving monitoring and automatic alarm controlemergency shutdown (ESD) in situation with the destination ofdeformations of Yield Stress, Specified Minimum Yield Stress (SMYS),yield strain, Ultimate Tensile (UT) Strength, Rupture Pressure Ratio(RPR), buckling stress, fatigue limit under cyclic loading for fatiguecracks, or stress corrosion crack or cracking (SCC).

Some portions of the description which follows are explicitly orimplicitly presented in terms of algorithms and functional or symbolicrepresentations of operations on data within a computer memory. Thesealgorithmic descriptions and functional or symbolic representations arethe means used by those skilled in the data processing arts to conveymost effectively the substance of their work to others skilled in theart. An algorithm is here, and generally, conceived to he aself-consistent sequence of steps leading to a desired result. The stepsare those requiring physical manipulations of physical quantities, suchas electrical, magnetic or optical signals capable of being stored,transferred, combined, compared, and otherwise manipulated.

Unless specifically stated otherwise, and as apparent from thefollowing, it will be appreciated that throughout the presentspecification, discussions utilizing terms such as “scanning”,“calculating”, “determining”, “replacing”, “generating”, “initializing”,“outputting”, or the like, refer to the action and processes of acomputer system, or similar electronic device, that manipulates andtransforms data represented as physical quantities within the computersystem into other data similarly represented as physical quantitieswithin the computer system or other information storage, transmission ordisplay devices.

The present specification also discloses apparatus for performing theoperations of the methods. Such apparatus may be specially constructedfor the required purposes, or may comprise a general purpose computer orother device selectively activated or reconfigured by a computer programstored in the computer. The algorithms and displays presented herein arenot inherently related to any particular computer or other apparatus.Various general purpose machines may be used with programs in accordancewith the teachings herein. Alternatively, the construction of morespecialized apparatus to perform the required method steps may beappropriate. The structure of a conventional general purpose computerwill appear from the description below.

In addition, the present specification also implicitly discloses acomputer program, in that it would he apparent to the person skilled inthe art that the individual steps of the method described herein may beput into effect by computer code. The computer program is not intendedto be limited to any particular programming language and implementationthereof it will be appreciated that a variety of programming languagesand coding thereof may be used to implement the teachings of thedisclosure contained herein. Moreover, the computer program is notintended, to be limited to any particular control flow. There are manyother variants of the computer program, which can use different controlflows without departing, from the spirit or scope of the invention.

Furthermore, one or more of the steps of the computer program may beperformed in parallel rather than sequentially. Such a computer programmay be stored on any computer readable medium. The computer readablemedium may include storage devices such as magnetic or optical disks,memory chips, or other storage devices suitable for interfacing with ageneral purpose computer. The computer readable medium may also includea hard-wired medium such as exemplified in the Internet system, orwireless medium such as exemplified in the GSM mobile telephone system.The computer program when loaded and executed on such a general-purposecomputer effectively results in an apparatus that implements the stepsof the preferred method.

Table 1 shows details of the navigation data in the example embodiment.

TABLE 1 Field Description DD/mm/yy date Hh:mm:ss.ss 1PPS GPS time XF.xxEasting of drone YF.yy Northing of drone SF.xx KP of drone (Distancealong the structure) CFF Drone height XVV.x Drone heading sDVVV CPValues (Controlled Parameter)

Table 2 shows details of the magnetometric data in the exampleembodiment.

TABLE 2 Field Description DD/mm/yy date Hh:mm:ss.ss 1PPS GPS time H_(x)X-axis magnetometric value H_(y) Y-axis magnetometric value H_(z) Y-axismagnetainetric value

If an anomaly in the magnetometric data is found at the same time stamp,such anomaly is associated with the coordinates that have beendetermined. By compiling and processing all data collected from aninspection mission, locations of potential defects, which correspond tothe anomalies in magnetometric data, are determined in the exampleembodiment.

Furthermore, the system of the example embodiment is capable ofevaluating a danger degree of a defect, calculating a pipeline safeoperating pressure and calculating a structure safe operation term. Anintegral index F of danger degree of a defect that takes into accountthe extent of magnetic anomaly, amplitude and shape of distribution ofmagnetic field intensity vector over the background values is calculatedin the example embodiment based on the following formula:

F=A·ê(1−Q _(φ)/(Q _(AH)))   (1)

where A denotes a corrective coefficient characterizing influence ofdefects of pipelines upon the magnetic field change and is typicallydetermined after a calibration procedure; Q_(AH), Q_(φ) denote densityof magnetic field strength distribution along a structure axis inanomaly zone and in a “calm” background area A/_(m), respectively. Thedensity is typically determined as a length of a section of a curve.

In the example embodiment, the curve comprises a geometrical place ofpoints of intensity of a magnetic field in space, thus:

dQ=√{square root over(dH _(x) ² +dH _(y) ² +dH _(z) ²)}  (2)

where dH_(x), dH_(y), dH_(z) denote values of change of magnetic fieldstrength vector. A/_(m) ², respectively.

In the example embodiment, Q_(AH) and Q_(φ) are calculated byintegrating dQ by length of anomaly and d background sections,respectively.

The calculated values of index F are maintained e.g. in a database ofrevealed defects, and also in diagrams of anomalies distribution. Table3 provides a ranking of sites (i.e. locations) with magnetic anomaliesbased their danger degree. On sites with the first danger rank, thefirst priority repair-reconstruction works are carried out. On siteswith the second danger rank, planned repair-reconstruction works arescheduled. On sites with the third danger rank, the operation of thepipeline is allowed without repair-reconstruction works.

TABLE 3 Danger degree of magnetic No Value of integral index F anomaly,rank 1 from 0 to 0.2 first 2 from 0.22 to 0.55 second 3 from 0.55 to0.99 third

Additionally, in the example embodiment, the safe operating parameterP_(safe) is calculated based on the respective danger degree of thedefect. The parameter can be stress, rust, stress fractures, corrosion,pressure, or another parameter.

For sections with defects of the first danger rank (i.e. 0≦F<0.2), atF<0.1:

P _(safe)=0.9 P _(oper)+0.1 P_(oper) ·F   (3)

at 0.1≦F<0.2: P _(safe)=0.9 P _(oper)+0.05 P _(oper) ·F   (4)

For sections with defects of the second danger rank (i.e. 0.2≦F<0.55):

P _(safe)=0.1 P _(oper)+0.05 P _(oper) ·F   (5)

For sections with defects of the third danger rank (i.e. F≧0.55):

P _(safe)=1.06P _(oper)+(0.95P _(design)−1.06P _(oper))·F   (6)

where P_(oper) denotes parameter in a structure at the moment ofinspection, measured in megapascals (MPa); P_(design) denotes designparameter in a structure (in MPa): and P_(safe) denotes calculated safeoperating parameter in a structure.

If the value of calculated safe operating parameter P_(safe) exceeds thedesign parameter P_(design), the structure is preferably operated at thedesign parameter. The assessment of structure technical condition canalso be carried out based on the coefficient of safe parameter—estimatedrepair factor—ERF (ASME), where:

ERF=P _(oper) /P _(safe)   (7)

In the example embodiment, at ERF≧1, a defect is assessed as extreme andsubject to the first priority repair.

For a structure short-term operation, the maximum admissible operatingparameter P_(max) (also known as MAOP) is calculated in the exampleembodiment:

P_(max) =P _(safe)·τ  (8)

where τ denotes a coefficient of the short-term increase of theparameter, which is determined by the operating organization and mayrange from 1.1 to 1.15 in the example embodiment.

The structure safe (i.e. accident-free) operation term T_(safe) iscalculated in the example embodiment on the condition that the structureis operated at the calculated safe parameter, as described above withrespect to Equations (3)-(6). After having repaired all revealed defectsthe structure safe operation term is fixed no more than 90% fromcalculated value lease explain what is meant by “fixed no more than 90%from each revealed defect, the calculations are carried out in theexample embodiment by the following formula:

T _(safe) =K _(p) ·K _(F) ·K _(t)   (9)

where K_(p) denotes a coefficient considering the pressure in thestructure, K_(F) denotes a coefficient considering danger degree of adefect; and K_(t) denotes a coefficient which takes into account theterm of a structure operation.

For example, if the structure is operated at the design parameter,K_(p)=1, otherwise:

Êδ=e 1−P _(design) P _(oper)   (10).

Also, K _(F)=−2 Lg 1−F   (11)

K_(t) considers the influence of operation factors in particular, theprobability of is structure failure within the first 3 years ofoperation because of construction-assembly detects and because ofcorrosion damage after 5-7 years of operation.

K _(t)=10·T·ΔT   (12)

where T denotes the normative operation term of a structure (measured inyears), and ΔT denotes the operation term of a structure since themoment of its putting into operation (measured in years).

Additionally, the method and system of the example embodiment can have ahigh sensitivity due to the non-contact registration of the structuremagnetic field and the filtration of relevant signal over noise. Thismeans that metal detects causing stress-deformed conditions aretypically not missed during inspection. Advantageously, the magneticfield change of the whole defective section (cluster)—not a separatedefect—is registered in the example embodiment. That is the method andsystem of the example embodiment can provide a quantitative assessmentof stress concentrator F for all interconnected defects of theregistered magnetic anomaly (or stress-deformed condition anomalyresulting from a cluster).

Furthermore, the method and system of the example embodiment canadvantageously be a single tool for inspection of structures ofdifferent sizes, and allow evaluating the danger degree of defects ofvarious types on the basis of the unified quantitative index F ofstress-concentrator value. Preferably, this allows calculating ERF forthe defects of “metal loss” type and other types such as “crack-likedefects”, weld defects, “continuity failure”, “geometry change”, etc.Thus, the calculations of serviceability for all types of defects—notonly “metal loss” type—can be made possible.

The method and system of the example embodiment can be implemented on acomputer system (700), schematically shown in FIG. 6. It may beimplemented as software, such as a computer program being executedwithin the computer system (700), and instructing the computer system(700) to conduct the method of the example embodiment.

The computer system (700) comprises a computer module (702), inputmodules such as a keyboard (704) and mouse (706) and a plurality ofoutput devices such as a display (708), and printer (710).

The computer module (702) is connected to a computer network (712) via asuitable transceiver device (714), to enable access to e.g. the Internetor other network systems such as Local Area Network (LAN) or Wide AreaNetwork (WAN).

The computer module (702) in the example includes a processor (718), aRandom Access Memory (RAM) (720) and a Read Only Memory (ROM) (722). Thecomputer module (702) also includes a number of Input/Output (I/O)interfaces, for example I/O interface (724) to the display (708), andI/O interface (726) to the keyboard (704).

The components of the computer module (702) typically communicate via aninterconnected bus (728) and in a manner known to the person skilled inthe relevant art.

The application program is typically supplied to the user of thecomputer system (700) encoded on a data storage medium such as a CD-ROMor flash memory carrier and read utilising a corresponding data storagemedium drive of a data storage device (730). The application program isread and controlled in its execution by the processor (718).Intermediate storage of program data maybe accomplished using RAM (720).

It will be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

What is claimed is:
 1. A drone mounted system for inspecting astructure, comprising: a. a movable drone mounted magnetometrictomography method (MTM) module for detecting a defect or stress alongthe structure; b. an altimeter sensor for determining a height of thedrone mounted MTM module to locate the defect, and c. a calculation unitfor categorizing the defect with a ranging of dangerous as one of one,two, and three corresponding to immediate repair, scheduled repair, andno repair.
 2. The system as claimed in claim 1, wherein the modulecomprises a sensor array with at least three sensor positioned in threeorthogonal dimensions.
 3. The system as claimed in claim 2, furthercomprising a compass for registering azimuth data of the defect andstress position on the structure at the determined height.
 4. The systemas claimed in claim 2, the system outputting a 3D map of the inspectedstructure on a computer screen; the map showing the defects and stressconcentrator.
 5. The system as claimed in claim 2, wherein thecalculation unit is located in the module.
 6. The system as claimed inclaim 5, wherein the calculation unit is in wireless communication withthe module.
 7. The system as claimed in claim 6, further comprising acamera for registering an image of the defect, which is visible ornon-destructive testing (NDT) or non-destructive examination (NDE) toolsfor hidden defects and internal anomalies, including corrosion, weldcracs, and delaminations.
 8. The system as claimed in claim 7, whereinthe calculation unit is further configured to account for stressconcentration, stress effect, material strength, condition stresseffect, or stressing sequence.
 9. The system as claimed in claim 7,wherein the calculating unit determines a safe operating parameter ofthe structure.
 10. The system as claimed in claim 1, wherein thecalculation unit determines a safe operation term of the structure. 11.The system as claimed in claim 2, further comprising a globalpositioning system (GPS) unit and/or a height sensor for determining aposition of the drone mounted MTM module relative to a ground surface ora structure surface and relative to a linear coordinate of structureaxis comprising at least one of an odometer, a Doppler velocity log anda microelectromechanical systems (MEMS) accelerometer coupled to thedrone mounted MTM module.
 12. The system as claimed in claim 2, furthercomprising an engine for moving the sensors along the structure adjacentto the structure.
 13. The system as claimed in claim 12, wherein adistance between the sensors and a surface of the structure is from 0,being on the structure surface, to a distance equal to 15 time adiameter or a width of the structure or a structural member of thestructure.
 14. The system as claimed in claim 13, further comprising arange finder to determine a distance between the sensors and the surfaceof the structure.
 15. The system as claimed in claim 14, furthercomprising a control unit to adjust operation of the engine in order tokeep the distance between the sensors and the surface of the structurefrom 0, being on the structure surface, to a distance up to 30 meters.16. The system as claimed in claim 1, further comprising a control unitto adjust operation of an engine of the drone mounted MTM in order tokeep the distance between the sensors and the surface of the structurefrom 0, being on the structure surface, to a distance equal to 15 time adiameter of the structure.
 17. The system as claimed in claim 1, furthercomprising, monitoring an automatic alarm control ESD in situation withthe destination of deformations of Yield Stress, Specified Minimum YieldStress (SMYS), yield strain, Ultimate Tensile (UT) Strength, RupturePressure Ratio (RPR), buckling stress, fatigue limit under cyclicloading fur fatigue cracks, or stress corrosion crack or cracking (SCC).18. A method for inspecting a structure, the method comprising the stepsof: a. detecting a defect or stressing along the structure using a dronemounted magnetometric tomography method (MTM) module adjacent to thestructure; b. determining a height of the drone mounted MTM module byuse of an altimeter sensor; c. determining a position of the dronemounted MTM module, thereby determining the position of the defect orstress concentrators, and d. categorizing a danger of the defect as oneof one, two, and three corresponding to immediate repair, scheduledrepair, and no repair.
 19. The method as claimed in claim 18, whereinthe step of determining the position of the drone mounted MTM modulecomprises: a. determining the position of the drone mounted MTM modulerelative to a ground surface or a structure surface; and b. determiningan absolute position of the drone mounted MTM.
 20. The method as claimedin claim 19, further comprising synchronizing time stamps of data fromthe drone mounted MTM module and equipment for determining the positionof the drone mounted MTM module based on a GPS time signal.
 21. Themethod as claimed in claim 20, further comprising categorizing thedefect based on at least a density of magnetic field strengthdistribution along a structure axis in an anomaly zone.